1. Field of the Invention
This invention relates to a displaying medium allowing the repeated setting of a security image in a display/undisplay state or in a mechanically readable/unreadable state by, for example, reversibly recording and erasing the image, a recording apparatus using the displaying medium, and an entrance/exit control system using the displaying medium.
2. Description of the Related Art
Recently, magnetic cards and IC cards with an information storing section have been used in various applications such as telephone cards, prepaid cards, or ID cards.
As such cards are used more and more, however, there arise problems such as forged cards, illegally altered cards, or unauthorized use of cards. Because of such problems, there are strong demands for an assurance of the security of the card and the card-based system.
To cope with such problems, a method has been proposed which provides a card with pieces of information used to examine the truth of the card and combines the pieces of information to increase the security.
For example, an IC card has been proposed which has a display section carrying a visible image or a bar code on its surface and which causes the visible image or the bar code to correspond to the information read from its built-in memory circuit (for example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-174171).
This proposed card, however, has the problem that the card can be forged by copying the memorized information and clipping the display section carrying an visible image or a bar code and pasting it on a forged card.
Further, an authenticity checking method has been proposed in which a picture element or an image (hologram) sensible only when illuminated by reference light of a specific wavelength, is printed in a specific position on the surface of a card with a memory section, information is written in the card in the form of converted data encoded using the positional data on the picture element or image, and when the data is to be read, the positional data on the picture element or image is sensed by projecting the reference light, and the card is checked by collating the data obtained by inverse conversion, using the positional data, of the stored converted data with the previously entered data (for example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-212790).
Although this proposal provides excellent security control, it requires a special light source and a special sensor, resulting in a complicated apparatus. Thus, there is the danger that a decrease in the reliability of the apparatus due to its complexity degrades the security.
Further, there is a card that allows the recording of a using state on the card in a visible manner so that the user can check the present using state of the card.
Because in such a card, the capacity of its recording section in which the using state is recorded is limited, the card must be reissued when the recording section has no space left in the course of recording even if the card is still valid.
To overcome this problem, a card has been devised in which the recording section is made of a reversible recording material so that the using state can be rewritten many times (for example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-116594 or Jpn. Pat. Appln. KOKAI Publication No. 3-218898).
Cards of this type have the advantage that they enable repeated recording and erasing of an image but have the disadvantage that their security is low because the image itself can be rewritten and forged easily.